This invention relates to apparatus for sorting fibrous stock suspensions, e.g. of wood pulp, particularly for eliminating particulate impurities.
In many operations performed in connection with suspensions of fibrous material in a liquid, it is desirable to treat the suspension of fibrous material to provide a resultant suspension which contains fibers that are free of impurities.
A known structure for sorting fibers and for removing impurities comprises a closed container, preferably operating in a vertical condition and preferably having a structure which is generated around an axis of rotation. The structure may thus be in part conical, in part cylindrical and in part of other shapes which are, however, symmetrical about the vertical axis.
An inlet line opens tangentially into the container. A device is provided to form a vortex in any liquid which is injected tangentially into the container. The vortex creating device is preferably a rotor within the container. The rotor is located adjacent a strainer through which the treated, fibrous stock suspension is caused to pass to an outlet line.
The container is also provided with a plurality of discharge openings. One of the discharge openings discharges fluid containing impurities which are relatively heavy. Another discharge opening delivers fluid containing impurities which are relatively light. An outlet delivers fluid free of the heavy and light weight impurities.
Because a vortex is created, the heavier impurities are driven by centrifugal force to the circumferential area of the container where the outlet for the heavy impurities is located. The light weight impurities are driven by the vortex to another area, preferably at the center of the vortex where the fluid carrying these particles may pass through another outlet. The remaining fluid which has thus been purified of the contaminants passes through the outlet.
A device of the above kind has been described for example in Austrian Application No. 9203/76. In that device, the fibrous stock suspension is treated in the container for removal of impurities. In that prior device, fibers which had not yet been broken down were beaten further by the rotor in the container and were then forced through a strainer located just downstream of the rotor in the flow path. The supply line delivered fiber suspension upstream of the rotor. Due to the tangential inlet direction of the suspension to be purified and to the operation of the rotor, centrifugal force was produced by means of which the heavier impurities were conducted principally down along the container wall to a discharge opening. Light weight impurities gathered in the vicinity of the longitudinal axis of the container and were drawn off from there through the hollow shaft of the rotor.
However, this prior device has the disadvantage that impurities, and particularly the light weight impurities, were also broken down by the rotor so that it was possible for them to pass through the strainer and thus remain in the supposedly purified fibrous stock suspension.